Understanding the blue color in antique mosaic mirrored glass from the Temple of the Emerald Buddha, Thailand
Bruce D. Ravel, Wantana Klysubun, Christoph Hauzenberger, Prapong Klysubun, Yuying Huang, Weeraya Wongtepa, Panidtha Sombunchoo
Two samples of the blue glass produced in the middle 19th century from the Temple of the Emerald Buddha in Bangkok, Thailand, were studied in order to understand the origin of its blue color. The oxide components and trace elements are quantitatively determined by SEM-EDX/WDX and LA-ICP-MS techniques. The results indentify the lead glass composition as 50SiO2-25PbO-6.6Na2O-5.5CaO in wt%. The 3d transition elements detected include iron (1.0-1.3 wt% FeO), manganese (0.24 wt% MnO), cobalt (0.11-0.14 %wt CoO), and copper (0.07 wt% CuO). Combined analyses of X-ray absorption near edge structures and optical absorbance lead to a conclusion that the antique glass is primarily colored in blue by the divalent cobalt with additional yellow coloration due to the trivalent iron. The tetrahedral coordination geometry of these two species was deduced from the XANES pre-edge intensity and the observed absorption bands of their d-d transitions. The redox ratios of Fe2+/Fe3+, Mn2+/Mn3+, and Cu1+/Cu2+ in the original blue glass and the reference glasses were determined by the K-edge XANES analysis. The blue color of the antique glass can be reproduced in a laboratory glass on the basis of composition and melting conditions.